Hi folks,
I am creating wall assembly layers for baseline case. I am using DC energy code not LEED. But thought of taking help from the wisdom of this forum.
As per code, I trying to create assembly layers to get U-0.058. The materials per code are Stucco(R-0.08), two layers of Gypsum board (R-0.56+R-0.56), insulation (R-15+R-8 c.i.), interior air layer (R-0.68). The effective cavity insulation R-value for R-15 is 6.4 as per table, combining all layers, I am getting R-16.28 or U-0.061.
That is, R-total=0.08+0.56+6.4+8+0.56+0.68=16.28; U-total=0.061
Could somebody help me on this? how do I get U-0.058 using these layers? Kindly enlighten me if I am missing something.
Thanks,
John
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5902 thumbs up
November 5, 2021 - 10:27 am
Depending upon the software you are using there are usually more than one option for how you enter the wall U-values. Instead of the layer-by-layer method is it possible to simply enter a U-value for the assembly as a whole?
Jamy Bacchus
Associate PrincipalME Engineers
24 thumbs up
November 13, 2021 - 2:27 am
are you including the exterior air film? i don't see it in your calc. see 90.1's Appendix A A9.4.1 Air Films.
what's your framing? is it wood or metal stud? what spacing and what depth?
You can look at the 90.1 lookup tables in Appendix A to see if your assembly should be 0.058, but for building walls you can do this within the software either by layers or usually a simplified approach.
you can also check out other tools and resources:
none of these will deal with the thermal bridging calcs now part of the DC code. at some point you might want this great free guide:
Building Envelope Thermal Bridging Guide (BETB) v1.4